Our research concerns the migration and differentiation of the neural crest cells. We have used for this investigation a cell marking technique devised by the chief investigator of this proposal (N. Le Douarin, 1969, 1973, 1975), and based on structural differences between the interphase nucleus of two species of birds, the chick and the quail. The contribution of the cephalic neural crest to the organogenesis of the head and neck has been demonstrated in chimeric embryos which had received heterospecific grafts of fragments of the neural tube before the onset of neural crest cell migration. New derivatives of the neural crest have been found: the calcitonin producing cells of the ultimobranchial body, the carotid body glandular cells, the musculo-connective wall of the large arteries deriving from the aortic arches, the bones and cartilages of the face and of the visceral arches, the dermis of the face and of the ventral side of the neck. The differentiation of the autonomic neurons has been investigated. It was shown through biochemical, cytochemical and physiological approaches that the evolution of the ganglioblasts in adrenergic or in cholinergic neurons depends on the tissue environment which they are submitted to when they have reached their definitive site. This question will be the main subject of our investigations during next year. On the other hand we are developing clonal cultures of neural crest cells in order to test their differentiating capabilities and to study thier progressive determination. BIBLIOGRAPHIC REFERENCES: Le Douarin (N.M.), Renaud (D.), Teillet (M.A.) and Le Douarin (G.H.) - 1975 - Cholinergic differentiation of presumptive adrenergic neuroblasts in interspecific chimaeras after heterotopic transplantations. Proc. Nat. Acad. Sc., 72, 728-732. Le Douarin (N.M.) - 1975 -Extracellular factors controlling the migration and differentiation of the ganglioblasts of the autonomic nervous system. International Santa Catalina Island Colloquium. In "Extracellular matrix influences on gene expression", H.C. Slavskin and R.C. Greulich eds., Academic Press, New York, 591-599.